DETROIT — New documents reveal General Motors redesigned faulty ignition switches without changing the part number in more than the 2.59 million small cars at the center of its recall crisis.

Some of those additional vehicles underwent an ignition switch redesign as far back as 2004, GM said in a July 16 letter to regulators that was posted online Friday by the National Highway Traffic Safety Administration. In some cases, the part number wasn't changed as would be required.

It's possible that the old parts remained in circulation and were used to service vehicles, GM said. The vehicles identified in the filing are among an additional 7.6 million the company flagged on June 30 for ignition-related issues.

Chief Executive Officer Mary Barra, who took over in January, has been making the case that the automaker's corporate culture regarding safety has changed. Barra has been called before Congress four times this year after it was determined the Detroit-based company waited at least a decade to recall millions of vehicles for ignition switches that could be inadvertently shut off when jarred, cutting power to the engine and deactivating air bags.

Barra told House and Senate panels in April that when a part is redesigned it should be assigned a new part number. "It is crucial," Barra said during an April 2 Senate hearing. "It's engineering principle 101 to change the part number when you make a change."

The ignition-switch recall began in February with about 2.59 million cars, including the Chevrolet Cobalt. Following the Cobalt recall, the largest U.S. automaker stepped up its review of potential safety issues and has recalled almost 29 million vehicles in North America this year, a record. About 17 million of the fixes have dealt with ignition issues including more than 12 million flagged in June alone.

GM's internal investigation into the Cobalt said that engineer Ray DeGiorgio authorized a change to the ignition switch in the Cobalt in 2006, while also approving that the new part keep the old part's number. That move ran counter to GM policy and confounded company investigators for years afterward, according to the internal company investigation. He was one of 15 employees ousted following the three-month long investigation, which was led by former U.S. Attorney Anton Valukas and released in June.

Sen. Richard Blumenthal, a Connecticut Democrat, pressed GM on Thursday to broaden the victim-compensation program set up by the automaker to include other victims of ignition-switch defects beyond the 2.59 million small cars.

Barra told senators during a hearing Thursday that it wouldn't be appropriate to include owners of cars other than the Cobalt, Ion and four other U.S. models.

"I would say there's very different facts related to what happened with the Cobalt ignition-switch situation versus the other actions we've taken," Barra said. "Very different."

GM's July 16 letter to NHTSA updated its timeline for the additional 7.6 million vehicles it recalled for unintended ignition key rotation.

Page 2 of 2 - The automaker alerted dealers in May 2003 about potential stalling issues in the Chevrolet Malibu, Oldsmobile Alero and Pontiac Grand Am for model years 1999-2003. Dealers were asked to "pay attention to the key size and mass of the customer's key ring." In July, GM ordered an engineering change to the switch to increase the detent plunger force.

While the part number was changed in those cases, the old part number was designated as "use," making it possible that the faulty switch was used to fix other vehicles, GM said.

In 2004, GM ordered an engineering change on switches used on the Pontiac Grand Prix to increase detent plunger force. In this case, GM didn't change the part number.

DeGiorgio, the GM engineer in the Cobalt, was responsible for approving the changes with these switches as well, Alan Adler, a GM spokesman, said Friday. Adler said he doesn't know why GM didn't conduct a recall in 2003 or 2004.

The updated timeline shows GM didn't review the issue until May of this year, when a products-investigation engineer was asked to look at ignition switches on the 1999-2003 Malibu, Grand Am and Alero. The investigation grew to include other models. From June 13 through June 24, GM tested cars at its proving ground in Milford, Mich.

Road testing showed, when key rings were sufficiently heavy they could stall, "when a vehicle goes off road or experiences some other jarring event."

In the case of the Chevrolet Cobalt and Saturn Ion, GM has instructed owners to remove extra keys and their key chains until they can get the recall repairs done. The remedy is a new, redesigned switch.

With the Malibu, Alero, Grand Am, Grand Prix and three other models — the Oldsmobile Intrigue, the Chevrolet Impala and the Chevrolet Monte Carlo — GM is stopping short of replacing the switch. It's installing key rings and adding a cover to the ignition key.

"It's not a question of having bad parts and recall parts, we believe from extensive testing, we believe that the remedy that we put forward is the right one and it will be more than sufficient," Adler said.